The present invention relates to the field of the colouration of ophthalmic lenses. More particularly, the invention relates to a novel design for the multi-tint colouration of ophthalmic lenses.
Within the meaning of the invention, by “ophthalmic lenses” is meant corrective and non-corrective lenses and also masks and other vision devices intended to be worn in front of the eyes.
The structures involved in vision are well known: these are the photoreceptors of the retina of the eye, namely the cones and the rods, which are responsible for the conversion of light energy into nerve impulses. The cones have a threshold of sensitivity to bright light, contain three different pigments (blue, green, red) and are therefore sensitive to colours, and make it possible to distinguish details: they are therefore suited to daytime vision. Conversely, the rods possess a very low light detection threshold (one photon) and are suited to night vision.
When the eye is suited to a low-light environment, it is mainly, or even solely, the rods which ensure the acquisition of visual information. This adaptation of the retina to darkness, linked to a phenomenon of rhodopsin regeneration, is optimum on average after 20-30 minutes spent in total darkness. The more prolonged this adaptation of the retina to darkness, the more immediate its loss of adaptability: a brief glare will immediately cause saturation of the rods situated in the zone exposed to the glare, and the recovery of the eye's maximum night vision capacities, in this zone, by a slow rhodopsin regeneration will require at least another twenty minutes.
The rods, numbering approximately 120 million in total, are situated in the peripheral zone of the retina surrounding a central zone, approximately 4 mm in diameter, called the macula and constituted exclusively by cones.
Driving a vehicle is a multisensory task in which the information picked up by the eye is essential for the driver to reach a prompt and appropriate decision. Under difficult visual conditions, during night driving for example, this activity becomes more difficult and the risks of accidents are higher.
Several needs have thus been identified by the applicant to optimize night vision and therefore improve the driver's comfort and safety.
Firstly, it is necessary to obtain effective protection against glare, in order to maintain so far as possible the adaptation of the retina to darkness. Glare phenomena, which are frequent during night driving, associated for example with the headlights of vehicles coming in the opposite direction or being reflected in the rear-view mirrors, are due more to the great difference between the intensity of the dazzling light and the eye's level of adaptation to darkness than to the intrinsic value of the intensity of the light source. In other words, the same headlights causing a nuisance at night will have only a slight effect in the daytime, the retina being already accustomed to seeing bright objects.
The rods, sensitive to wavelengths between 450 nm and 530 nm, are practically not stimulated by a source of red or orange light (wavelengths greater than 600 nm). The protection of the eyes by a red or orange filter almost exclusively allowing light of wavelengths greater than 600 nm to pass through should thus make it possible to prevent rhodopsin degradation and to maintain the adaptation of the eye to darkness.
Secondly, it is necessary for the driver to be aware of his environment, such as for example road signs, in a detailed and contrasted manner. Numerous works have shown that yellow filters, selectively cutting out the short wavelengths (i.e. the blue light), improve sensitivity to contrast. Such filters are in particular described in Wolffsohn et al., Optometry and Vision Science, volume 77(2), pages 73-81, (2000). The works of Wolffsohn show that cutting out the short wavelengths with yellow filters increases contrast perception, in particular when viewing luminous objects against an overall blue background.
It would thus be desirable to have spectacles with lenses providing both effective protection against glare and the subsequent degradation of the rhodopsin of the rods, and an improvement in the perception of contrasts by filtering out of blue light with a short wavelength.
Several patents describe lenses comprising a grey or dark zone on part of their surface making it possible to reduce the glare produced by vehicle headlights or external lights which are too strong. Such lenses are described in GB 277167, JP 9005681 and DE 19650122. These patents correspond partially to just one of the needs of night vision, protection against glare: the grey tint reduces the overall level of transmission of the light rays but does not specifically filter out the rays responsible for the phenomenon of the eyes' loss of adaptability, namely the light rays having wavelengths of less than 600 nm.
U.S. Pat. No. 5,428,409 describes spectacles for night driving comprising a glare-reducing dark-tinted zone situated in the upper quarter of the spectacle lens and a light-transmission zone, optionally coloured yellow, covering the remainder of the surface of the lens.
FR2684771 proposes a double-tint solution. An “iridescent violet or derivatives” colour in the top part of the lens and a yellow tint in the bottom part of the lens for clear and contrasted vision. The teaching of this prior art is however equivocal. In fact, this document claims that the violet zone in the upper part of the lens selectively allows the red light (with a long wavelength) to pass through. Now, it is known that the violet radiation, by contrast, is radiation with a short wavelength (approximately 400 nm) to which the rhodopsin of the rods is very sensitive. Moreover, in this document the “anti-glare” zone is present only in the upper half of the lens and cannot therefore protect all of the rods distributed over the entire peripheral zone of the retina. On the other hand, the yellow tint is limited to the lower part of the lens and does not therefore make it possible to improve sensitivity to contrast for the perception of objects situated, in terms of far vision, straight ahead of the driver, such as road signs or obstacles to be avoided on the carriageway, or only at the cost of a significant and uncomfortable change in the position of head.
None of the documents of the prior art, to the applicant's knowledge, therefore describes ophthalmic lenses which are perfectly suited to night vision, i.e. lenses making it possible both to protect the rods situated on the periphery of the retina against exposure to wavelengths less than approximately 600 nm and to improve the perception of contrasts in the zone of the lens covered by the view and passed through by the light rays which arrive at the cone-rich macula.